The present invention relates to electro-pneumatic brake control systems for railroad freight trains and in particular, to microprocessor based electro-pneumatic brake control systems that employ pressure transducers for feedback in controlling operation of the individual car brakes.
Present day freight trains have a brake pipe that runs through each car and is coupled therebetween so as to extend continuously the length of the train. The brake pipe is charged with compressed air typically at the head end by a compressor on the locomotive. The compressed air not only supplies stored energy to provide the pneumatic brake force at the respective cars, but also serves as a communication link via which the car's brakes are controlled from the locomotive. Brake application and release signals are transmitted by increasing and decreasing the brake pipe pressure.
Due to the length of modern day freight trains, considerable time is required for the pneumatic control signals to propagate from the front to the rear cars of the train. This can present difficulty in controlling the train, particularly on long trains operating over undulating terrain, due to the time delay in brake response between head and rear end cars. Accordingly, microprocessor based electro-pneumatic brake control has been proposed to obtain near instantaneous brake response on all the cars of the train. Near-instantaneous remote control of the car brakes may be accomplished either by means of radio signals or by a train line wire, for example.
A microprocessor on board each railroad car receives the electrically transmitted brake control signals and operates solenoid valves that may be arranged to regulate the car brake cylinder pressure either directly or indirectly. In directly controlling the brake cylinder pressure, a reservoir charged from the train brake pipe provides a source of compressed air with which to charge the car brake cylinders via an application solenoid valve. In the indirect control arrangement, compressed air carried in the train brake pipe is exhausted locally via a solenoid valve to cause the car control valve device to operate in a well-known manner to apply the car brakes.
In either of the foregoing arrangements, near-instantaneous remote control of the car brakes is accomplished and the respective car brakes are operated concurrently. The resultant uniform brake response, therefore, has the potential to provide greatly improved train performance.
In both of the foregoing control arrangements, pneumatic pressure to electric transducers are employed to provide feedback information to the car microprocessor such that the brake response is appropriate in terms of the electrically transmitted brake control signals. It will be appreciated, therefore, that in order to realize the potential that electro-pneumatic control of a railroad freight train offers, this feedback information provided by the pressure transducers must have reasonably high accuracy. While statistically it can be expected that a fairly high percentage of these transducers will provide sufficiently accurate pressure readings, in practical terms, it can not be expected that all of such transducers will always provide such accuracy.